1. Field of the Invention
The present invention relates to a fuel injection valve mainly used in a fuel supply system of an internal combustion engine. Particularly, the present invention relates to an improvement of an electromagnetic fuel injection valve comprising: a valve housing which includes: a valve seat member having a valve seat at a front end thereof; a magnetic cylinder connected coaxially to a rear end of the valve seat member; a nonmagnetic collar connected coaxially to a rear end of the magnetic cylinder; and a stationary core fittingly fixed to a rear part of the nonmagnetic collar; a valve assembly including: a valve element capable of being seated on the valve seat; and a movable core connected to a rear end of the valve element and facing an attraction surface of a front end of the stationary core; a valve spring for urging the valve assembly in a direction in which the valve element is seated on the valve seat; the valve assembly and the valve spring being housed in the valve housing, a coil assembly disposed so as to surround the nonmagnetic collar and the stationary core; a magnetic coil housing which houses the coil assembly, and magnetically connects the magnetic cylinder and the stationary core to each other; and the coil housing including: a shell part surrounding the coil assembly; a front end wall part facing a front end of the coil assembly; and a boss part press-fitted to an outer peripheral surface of the magnetic cylinder, the shell part, the front end wall part and the boss part are integrally connected together.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2006-2636 discloses such an electromagnetic fuel injection valve.
In most of the conventional electromagnetic fuel injection valves, a coil housing is molded from a magnetic metal plate by ordinary press-molding, and its shell part, front end wall part, and boss part have a substantially uniform thickness. However, in the front end wall part, the annular magnetic path area decreases toward the inner peripheral, and thus magnetic flux saturation occurs in the inner peripheral portion thereof, providing a factor to hinder improvement in characteristics of attraction force between a stationary core and a movable core. Also, in the conventional electromagnetic fuel injection valves, the front end of a coil assembly is supported by the front end wall part of the coil housing to define the axial position of coil assembly. Because the coil housing is press-fitted to the outer peripheral surface of a magnetic cylinder, a minor positional displacement occurs between the magnetic cylinder and coil assembly due to a press-fitting error, and this positional displacement makes unstable the characteristics of attraction force between the stationary core and the movable core.